<b>Aims/hypothesis</b>: Maturity Onset Diabetes of the Young (MODY) is a rare monogenic form of diabetes. In 2009, >80% of UK cases were estimated to be misdiagnosed. Since then, there have been a number of initiatives to improve the awareness and detection of MODY including education initiatives (Genetic Diabetes Nurse (GDN) programme), the MODY probability calculator, and targeted next generation sequencing (tNGS). We aimed to examine how the estimated prevalence of MODY, and other forms of

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... nogenic diabetes diagnosed outside the neonatal period, has changed over time and how the initiatives have impacted case finding. <p><b>Research design and Methods: </b>UK referrals for genetic testing for monogenic diabetes diagnosed >1y of age from 01/01/1996 to 31/12/2019 were examined. Positive-test rates were compared for referrals reporting involvement of the GDNs/MODY calculator with those that did not.</p> <p><b>Results</b>: A diagnosis of monogenic diabetes was confirmed in 3860 individuals, >3-fold higher than 2009 (01/01/1996-28/02/2009; n=1177). Median age at diagnosis in probands was 21y. GDN involvement was reported in 21% of referrals; these referrals had a higher positive-test rate than those without GDN involvement (32% v 23%, p<0.001). MODY calculator usage was indicated on 74% of eligible referrals since 2014; these referrals had a higher positive-test rate than those not using the calculator (33% v 25%, p=0.001). 410 (10.6%) cases were identified through tNGS<i>. </i>Monogenic diabetes prevalence was estimated to be 248 cases/million (double that estimated in 2009 due to increased case-finding).</p> <p><b>Conclusions: </b>Since<b> </b>2009, referral rates and case diagnosis have increased three-fold. This is likely to be the consequence of tNGS, GDN education and the MODY calculator.</p>